Compared to adults, children show superior recovery of language function after damage to the dominant brain hemisphere. Possible explanations are that children have different patterns of language representation or display different patterns of reorganization. Information about language lateralization in children could provide insights into the repair mechanisms of the young brain. While functional magnetic resonance imaging (fMRI) is usually difficult to perform in children younger than 5 years, functional transcranial Doppler sonography (fTCD) is nonfrightening and readily applicable in young and very young children. However, for serial examinations, sufficient validity and reliability are required. To this end, we designed a picture-description language task (PDLT) for fTCD examinations in children, compared the outcome to established protocols and determined the 1 month retest-reliability of the measurement in 16 children aged 2-9 years. The dependent variable was the task-related hemispheric perfusion difference based on averaged relative cerebral blood flow velocity (CBFV) increases in the middle cerebral arteries. This picture-description language lateralization index was compared to language lateralization by a phonetic word generation task (PWGT) in adults revealing good intermethod validity (r=0.70; P <or= 0.05). The 1 month retest-reliability of the PDLT in the children was r=0.87 (P <or= 0.05). With this degree of reliability, fTCD seems a promising tool for the assessment of changes in hemispheric involvement in language in young and very young children.